The present invention relates to a multicolor liquid crystal display device utilizing a color filter formed by electrodeposition, and relates to the method of making the multicolor liquid crystal display device having high durability while being driven by a reduced driving voltage.
FIG. 2 shows one example of the conventional multicolor liquid crystal display device utilizing an electrodeposited color filter. In FIG. 2, the device is comprised of a transparent substrate made of glass, electrodes 12 made of transparent electroconductive film patterned in a desired shape, and color filters 13 formed by electrodeposition of a composition including electrodepositable polymer and coloring material. Each section of color filter 13 is superposed in alignment with the pattern of a corresponding section of electrode 12 and colored in a different color tone. The method of making color filter has been disclosed in Japanese Patent Application No. 233933/1982, and provides an efficient process of conveniently producing color filter having high resolution.
A transparent electroconductive film 14 made of indium-tin-oxide (ITO) is formed on the filter and patterned in alignment with each section of the electrode 12. An alignment layer 15 composed of polyimide is superposed on the electroconductive film 14. A second transparent substrate 16 is formed with a second transparent electrode 17 and another alignment layer 18. A liquid crystal 10 is filled in a space sandwiched by the pair of substrates 11 and 16 to constitute a liquid crystal cell.
The liquid crystal cell is applied with a driving voltage. When observing the liquid crystal cell through a polarizer and an analyzer which sandwich therebetween the cell, a part of the liquid cell in transparent state exhibits color tone of the color filter and the other part thereof does not pass incident light to exhibit black tone. Namely, the color liquid crystal display device displays different tones of the color filter by using the liquid crystal cell as an optical shutter.
In such a multicolor liquid crystal display device, the transparent electroconductive film 14 is used as a driving electrode, the electroconductive film 14 is not covered with an insulating film such as a color filter, hence any voltage drop is not caused by such color filter and therefore the driving voltage can be reduced.
However, the multicolor liquid crystal display device shown in FIG. 2 has a problem in view of reliability or durability with respect to the strength of the boundary between the color filter and the transparent driving electroconductive layer. If external stress is concentrated at the boundary due to, for example, heat, it may cause the transparent driving electroconductive film to fail and the generation of cracks. For example, a color filter formed by electrodeposition of polyester-melamine resin has a thermal expansion coefficient on the order of about 10.sup.-4, and a transparent driving electroconductive film of ITO formed thereon has a thermal expansion coefficient on the order of about 10.sup.-7. Such a difference of thermal deformation may cause a considerable amount of stress in the boundary of the color filter and ITO film due to an external factor such as temperature variation and thereby degrade the reliability of the device.
Aside from above, there has been proposed another type of conventional multicolor liquid crystal display device disclosed, for example, in U.S. Pat. No. 4,779,957 in which a color filter is formed on a base electrode provided on a substrate, and is covered with a protective layer. An alignment layer is disposed on the protective layer so as to absorb the stress between the color filter and the alignment layer by means of the interposed protective layer.